Newer diesel engines have diesel particulate filters (DPF) incorporated in their exhaust systems to filter carbon and other particulates from the exhaust gas stream. When enough particulate material has accumulated on the filter element, the DPF begins to become plugged and needs to be regenerated. Regeneration is a process whereby deposits on the filter element of the DPF are induced to combust, typically by raising the engine exhaust temperature if necessary by appropriate engine operations. The combustion event of a DPF regeneration harmlessly cleans the filter element of the DPF of deposits. The regeneration process repeats as often as necessary to maintain smooth and reliable engine operation.
In many diesel engines, an electronic control unit (ECU) controls and monitors the operation of engine components. The ECU typically sends commands various systems of the engine, including commands intended to trigger a regeneration of a DPF, under appropriate engine operating conditions. Some engine operating parameters are relayed to the ECU electronically and with the help of sensors. Usually, the ECU is capable of prematurely terminating the regeneration of a DPF if conditions suitable for safe and efficient regeneration cease to exist. One parameter of great importance to regeneration of the DPF is the rate of combustion of the deposits on the filter element during a regeneration event.
Typical engines monitor the rate of combustion of deposits in a DPF during regeneration by receiving input from temperature sensors located adjacent to a DPF. The temperature sensors are used to measure the temperature of exhaust gas exiting the DPF, and thus infer the heat released from the regenerative combustion of the deposits. Heat released during the regeneration is one indication of the rate of combustion of the deposits.
A possibility exists for damage to the DPF if combustion of the deposits on the filter of the DPF becomes uncontrollable and the internal temperature of the DPF goes above a threshold. Generally, a regeneration event may be terminated before completion if conditions conducive to an efficient regeneration cease to exist. However, controlling the elapsed time from the occurrence of uncontrolled regeneration to a premature termination is essential in preventing damage to the DPF. The sooner an uncontrolled regeneration is detected, the greater the possibility to cease the regeneration in a controlled fashion and avoid damage to the DPF.
A typical temperature sensor, such as those used to infer the rate of combustion in a DPF during a regeneration, has a response time that may not be sufficiently fast to avoid potential damage of the DPF under some conditions. A typical sensor can take up to 5 seconds before relaying a change in measured temperature. A 5 second delay may be detrimental to the ability of the ECU to terminate the regeneration when required. Another disadvantage of using temperature sensors to infer the rate of combustion in the DPF is heat absorption by the bulk mass of the DPF. Heat is absorbed by the bulk mass of the filter and surrounding casing of the DPF, thus further delaying the detected temperature increase in the exhaust gas downstream of the DPF.
Accordingly, there is a need for a faster and more reliable method of sensing a condition that may require the premature termination of a regeneration event in a DPF.